Unorganized individuals from twitter contacting your employer isn't harassment. If it is the implications would be scary the other way around: would you punish someone who pointed out a problem that happened to become popular on a social network?
That's not how cancelling works, except maybe in the case of celebrities. When you are canceled, no one calls and has a polite chat with your employer. They call and threaten your employer with arson. They find where you live and vandalize your home. It's harassment. It's illegal.
That line seems blurry to me. How do you define both and where is the line? I'm not sure that many angry emotional twitter users contemplate any line, I would assume most just think "I strongly disagree with that person's opinion or actions and I must punish them". I think most people would agree that harassment and doxing are bad, but I also think that most people would think that doing bad things to "bad" people is sometimes ok. Mobs of emotional people are not paragons of morality, bad actions by a few quickly spread and the morality of the mob normalizes to that new worse level.